1. Technical Field
This invention generally relates to electric discharge machines (EDM) and, more particularly, to a floating cover electrode guide system for use with an electric discharge machine, the electrode guide system guiding and precisely controlling the position of the electrode of the EDM.
2. Discussion
Electric discharge machines (EDM) are used to machine holes or features in production parts which require very small tolerances. When dealing with holes in the range of as small as 0.003" a variation of plus or minus 0.0005" is a 17% variation either side of nominal. Even though the absolute magnitude of the variation is relatively small, the percentage error would be beyond that acceptable for many production parts. For example, a plus or minus 2% variation in flow rate is an acceptable parameter on some injection nozzles which are machined using the EDM process. In light of these requirements, accurately controlling the position of and limiting the variation of the electrode location is critical. Obviously, a precision control guidance device is required within the industry to achieve the results required in such precise machine work.
In general, the EDM process is based on the principle of erosion of the metal work piece by spark discharges. The spark is an electric discharge through the space between the two charged elements, the first being the work piece and the second being an electrode. The work piece and the electrode are placed within a dielectric fluid. A direct current is applied to the system which includes a capacitor in parallel with the spark gap between the two elements. At low voltages the dielectric fluid acts as an insulator, but as the potential difference between the electrode and the work piece increases there is a dielectric breakdown in the fluid and a spark passes through the spark gap. The spark causes the vaporization of some of the work piece material as well as some of the material of the electrode. Following a spark discharge, deionization of the dielectric fluid reestablishes the insulation properties and the current again drops to zero. The capacitor is then charged again and the process begins over. This process can be repeated at a very high rate (200-500,000 cycles per second) with the metal removal rate being controlled by the current density or average current in the discharge circuit. Typically the higher the current density the rougher the surface finish but more material is removed.